Method of fabricating liquid crystal display device using a mixture of rubbing alignment material and UV alignment material

ABSTRACT

An LCD device includes first and second substrates, an alignment layer formed over at least one of the substrates, and a liquid crystal layer formed between the substrates. The alignment layer is formed of a mixture of rubbing alignment and UV alignment materials. A method of fabricating the LCD device includes preparing first and second substrates; coating an alignment layer over at least one of the substrates; performing a rubbing process on the substrate coated with the alignment layer; and irradiating polarized UV rays onto the substrate coated with the alignment layer, wherein the alignment layer is formed of a mixture of rubbing alignment a UV alignment materials. The rubbing process obtains high anchoring energy is obtained, thereby preventing afterimages. Also, the process of irradiating the polarized UV rays eliminates the problem of light leakage.

This application is a Divisional of co-pending application Ser. No.11/451,445, filed on Jun. 13, 2006 for which priority is claimed under35 U.S.C. §120 and which application claims the benefit under 35 U.S.C.§119 of Korean Application No. 10-2005-0051035, filed on Jun. 14, 2005,the entire contents of each of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

A liquid crystal display (LCD) device has at least one substrate with acoated alignment layer, and more particularly, to an alignment layer forinitial alignment of a liquid crystal in an LCD device.

2. Discussion of the Related Art

Ultra thin flat panel display devices have a display screen with athickness of several centimeters. Among these, LCD devices have beenwidely used for notebook computers, monitors, spaceships, aircrafts,etc. owing to their advantageous features of low driving voltage, lowpower consumption, portability, and the like.

Generally, an LCD device includes a color filter substrate having colorfilter layers formed thereon, a thin film transistor substrate facingthe color filter substrate and having thin film transistors formedthereon, and a liquid crystal layer formed between these substrates.

In such an LCD device, alignment of the liquid crystal layer is variedby applying a voltage to control transmittance of light, therebyallowing an image to be reproduced. Electrodes are thus formed on thethin film transistor substrate and/or the color filter substrate forapplication of the voltage such that a pixel electrode is located on thethin film transistor substrate, and a common electrode is located on thecolor filter substrate so as to generate a vertical electric fieldbetween the two substrates (for example, twisted nematic (TN) mode).Alternately, the pixel electrode and the common electrode are locatedparallel to each other on the thin film transistor substrate so as togenerate a horizontal electric field (for example, in-plane switching(IPS) mode).

FIG. 1 shows an exploded perspective view illustrating a related art TNmode LCD device.

As shown in FIG. 1, a thin film transistor substrate 10 includes a gateline 12, a data line 14 crossing the gate line 12, a thin filmtransistor T formed on a crossing region of the gate line 12 and thedata line 14, and a pixel electrode 16 connected to the thin filmtransistor T. A color filter substrate 20 includes a light-shieldinglayer (or black matrix) 22, R, G and B color filter layers 24 formed onthe light shielding layer 22, and a common electrode 25 formed on thecolor filter substrate 20.

A vertical electric field is generated between the pixel electrode 16 onthe thin film transistor substrate 10 and the common electrode 25 on thecolor filter substrate 20, thereby allowing alignment of liquid crystalsto be controlled.

Both substrates 10 and 20, constructed as described above, are bonded toeach other to form a single liquid crystal panel. At this time, a liquidcrystal layer is formed between the substrates 10 and 20.

Meanwhile, if the liquid crystal layer randomly aligns between thesubstrates 10 and 20, it is difficult to achieve a consistentarrangement of molecules in the liquid crystal layer. Thus, although notshown in the drawings, an alignment layer for the initial alignment ofliquid crystals is formed on the thin film transistor substrate 10and/or the color filter substrate 20.

Examples of a method for forming an alignment layer for initialalignment of the liquid crystal include a rubbing alignment method and aphoto-alignment method.

In the rubbing alignment method, after an organic polymer such aspolyimide is thinly coated on a substrate, a rubbing roll wound with arubbing cloth is rotated to rub the organic polymer, thereby arrangingthe organic polymer in a constant direction.

However, the rubbing alignment method has the following drawbacks.

First, when the arrangement of the rubbing cloth becomes disordered,problematic light leakage may occur. FIG. 2 shows a schematicperspective view illustrating a disordered arrangement of the rubbingcloth.

As described above, since the structure such as the thin filmtransistor, the color filter layer and the electrode layers are formedon the substrate, some portion 32 a of the rubbing cloth 32 wound aroundthe rubbing roll 30 can become disordered when the rubbing roll 30rotates on the structure formed on the substrate 10 or 20 as shown inFIG. 2. When the arrangement of the rubbing cloth becomes disordered,the chains of the organic polymer in a region rubbed by the disorderedrubbing cloth cannot be aligned, resulting in light leakage in thatregion due to non-uniform alignment of the liquid crystals.

Second, when the rubbing cloth fails to contact the substrate, theproblem-causing light leakage may occur. FIG. 3 shows a schematicperspective view illustrating an alignment state of the liquid crystalswhen the rubbing cloth fails to contact the substrate.

As described above, the electrode layers such as the pixel electrode andcommon electrode are formed on the substrate. Thus, as shown in FIG. 3,a region A where the rubbing cloth 32 fails to contact the substrate dueto a step on the substrate 10 is formed. In this case, the alignment ofthe liquid crystals is not uniform in the region A, thereby causing theproblem of light leakage.

In particular, in the TN mode LCD device, since the pixel electrode andthe common electrode are formed in pixel regions on differentsubstrates, respectively, there may not be very many regions having thesteps formed thereon. However, in the in-plane switching (IPS) mode LCDdevice, since the pixel electrode and the common electrode arerepeatedly formed in parallel in pixel regions on the substrate, thereare many regions having the step formed thereon, whereby the problem oflight leakage becomes serious.

The aforementioned problems in the rubbing alignment method are causedby the mechanism for providing physical contact between the rubbing rolland the substrate.

Recently, in order to solve these problems of the rubbing alignmentmethod, various studies have been conducted for providing a method formanufacturing an alignment layer that does not require physical contact.In particular, instead of using the rubbing alignment method, use of aphoto-alignment method has been suggested. In the photo-alignmentmethod, an alignment layer is produced by irradiating polarizedultraviolet (UV) rays onto a polymeric film. In order to align theliquid crystals, the alignment layer must have an anisotropic structure,which can be formed when the polymeric film anisotropically reacts withthe polarized UV rays.

However, although the photo-alignment method may address theabove-described problems related to the rubbing alignment methoddescribed above, the photo-alignment method has a serious problem inthat the anchoring energy is low. More specifically, with the rubbingalignment method, since the side chains of the organic polymer arearranged in the constant direction as described above, and grooves areuniformly formed over the surface of the substrate by rubbing, thealignment of the liquid crystals is controlled by mechanical interactionbetween the grooves and the liquid crystals as well as by chemicalinteraction between the side chains and the liquid crystals. Incontrast, in the photo-alignment method, the alignment of the liquidcrystals is controlled only by the chemical interaction between the sidechains and the liquid crystals caused only by the photoreaction, withoutforming grooves on the surface of the substrate. Accordingly, incomparison to the rubbing alignment method, the photo-alignment methodprovides a lower anchoring energy and causes a problem of afterimage.

Since the problem of afterimage caused by the photo-alignment method isserious to such an extent that the method cannot be applied tolarge-scale production lines, the rubbing alignment method has been usedfor large production lines in spite of the light leakage problems.

As LCD devices of a higher quality have been increasingly required,there is a need to developing a method of aligning the liquid crystalsthat can overcome or minimize the problems of the rubbing alignmentmethod and the photo-alignment method according to the related art.

SUMMARY OF THE INVENTION

Accordingly, the invention is directed to an LCD device and a method offabricating the same, which substantially obviate one or more problemsdue to limitations and disadvantages of the related art.

An object of the invention, in part, is to provide an LCD device and amethod of fabricating the same, in which problems of both the rubbingalignment method and the photo-alignment method can be solved.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of fabricating an LCD device includes preparing first and secondsubstrates; coating an alignment layer over at least one of thesubstrates; performing a rubbing process on the substrate coated withthe alignment layer; and irradiating polarized UV rays onto thesubstrate coated with the alignment layer, where the alignment layer isformed of a mixture of rubbing alignment material and UV alignmentmaterial.

In another aspect of the invention, an LCD device includes first andsecond substrates, an alignment layer formed over at least one of thesubstrates, and a liquid crystal layer formed between the substrates,where the alignment layer is formed of a mixture of a rubbing alignmentmaterial and a UV alignment material.

It is to be understood that both the foregoing general description andthe following detailed description of the invention are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 shows an exploded perspective view illustrating a related art TNmode LCD device;

FIGS. 2 and 3 illustrate problems of a related art rubbing alignmentmethod;

FIG. 4 illustrates a related art photo-alignment method using aphoto-decomposition reaction;

FIG. 5 illustrates a photo-alignment method using a photo-isomerizationreaction according to the invention;

FIG. 6 illustrates a photo-alignment method using a photo-dimerizationreaction according to the invention;

FIG. 7 is a sectional view illustrating an LCD device according to anembodiment of the invention; and

FIGS. 8A to 8E are process views illustrating a method of fabricating anLCD device according to an embodiment of the invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The invention addresses the problems of the conventional methods bycombining a rubbing alignment method and a photo-alignment method. Inother words, with the rubbing alignment method, when arrangement of arubbing cloth becomes disordered or the rubbing cloth fails to contactthe substrate, the alignment material coated on a region does not alignwith a constant alignment direction. Thus, the inventors of the presentapplication recognized this problem and conceived a method for causingthe portion(s) of the alignment material not aligned by the rubbingalignment method of the related art to be aligned by a photo-alignmentmethod configured to address this need. Also, using the rubbingalignment method solves problems relating to low anchoring energy in thephoto-alignment method.

Therefore, in order to use both the rubbing alignment method and thephoto-alignment method in the invention, the alignment layer is formedof a mixture of at least a rubbing alignment material and a UV alignmentmaterial.

If the mixed material of rubbing alignment material and UV alignmentmaterial is used, phase separation occurs between the rubbing alignmentmaterial and the UV alignment material when the temperature increases.Therefore, in order to prevent phase separation from occurring, therubbing alignment material preferably has polarity and structure similarto those of the UV alignment material.

The invention also utilizes, as the UV alignment material, a materialthat generates a photo-isomerization reaction or a photo-dimerizationreaction in the photo-alignment method. Hereafter, the photoreaction inthe photo-alignment method and the reason why the photo-isomerizationreaction or the photo-dimerization reaction is selected in the inventionwill be described.

The photo-alignment method may be classified into a photo-decompositionreaction, a photo-isomerization reaction, or a photo-dimerizationreaction depending on the kind of reaction between the utilizedalignment material and the UV rays.

In the photo-decomposition reaction, as shown in FIG. 4, when polarizedUV rays are irradiated to the polymer alignment layer, a connectionbetween side chains located in a polarized direction decomposes, andthus only the side chains vertical to the polarized direction remain,thereby allowing the liquid crystals to align in that direction.

In the photo-isomerization reaction, as shown in FIG. 5, when thepolarized UV rays are irradiated to the polymer alignment material, acis-state polymeric material can convert to a trans-state polymericmaterial, and vice versa. In the case of cis-state polymeric material,the side chains are aligned parallel to the substrate, so that theliquid crystals are aligned parallel to the substrate (homogeneousalignment). In the case of trans-state polymeric material, the sidechains are aligned vertical to the substrate, so that the liquidcrystals are aligned vertical to the substrate (homeotropic alignment).

In the photo-dimerization reaction, as shown in FIG. 6, when thepolarized UV rays are irradiated, double bonds (marked by an arrow)parallel to the polarization direction are broken and bond to adjacentmolecules. As a result, the liquid crystals align along the direction inwhich anisotropy is induced (that is, vertical or horizontal to thepolarization direction).

According to the photo-decomposition reaction of the photo-alignmentmethod, a first problem may occur in that anchoring energy is lowered asthe bonding of the alignment layer well aligned by rubbing decomposes.Second, afterimage occurs due to foreign matter generated by thephoto-decomposition reaction. Third, a step of removing the foreignmatter must additionally be provided to solve the problem relating toafterimage. In this case, a cleaning solution is required to remove theforeign matter, i.e., detritus, of the polymer material.

Therefore, the invention addresses the photo-isomerization reaction orthe photo-dimerization reaction of the photo-alignment method.

As described above, the invention combines the rubbing alignmentmaterial and the UV alignment material, where the rubbing alignmentmaterial has polarity and structure similar to that of the UV alignmentmaterial. In addition, the invention may use the material that generatesa photo-isomerization reaction or a photo-dimerization reaction, as theUV alignment material.

A polymeric material containing a polymer main chain and aphoto-reaction group connected to the polymer main chain is preferablyused as the UV alignment material.

The photo-reaction group is preferably selected from at least one of acinnamoyl based material, a chalcone based material, a coumarine basedmaterial, a maleimide based material, or an azo based material.

The polymer main chain is preferably selected from a polyimide, polyamicacid, polynorbornene, phenylmaleimide, polyvinylalcohol, polyamideimide,polyethyleneimine, polyamide, polyethylene, polystyrene,polyphenylenephthalamide, polyester, polyurethane,polymethylmethacrylate, an azo side-chain type imide, a stilbenemain-chain type imide, coumarine derivatives, and chalcone derivatives.Copolymers of these materials may also be used.

The rubbing alignment material is preferably at least one of polyimide,polyamic acid, polyamide, polynorbornene, polyamideimide, polyvinyl,polyolefine, polystyrene, polyacrylate, poly(vinylchloride), polyether,polyester, polythioether, polysulfone, polyethersulfone,polyetheretherketone, polyurea, polyurethane, polybenzimidazol,polyacetal, or poly(vinylacetate).

Also, in an exemplary method of fabricating an LCD device according tothe invention, the rubbing process and the UV irradiation process may beperformed simultaneously or separately (at different times). If therubbing process and the UV irradiation process may be performedseparately (at different times), the rubbing process may be performedbefore the UV irradiation process, and vice versa.

Furthermore, the UV irradiation process may be performed over the entiresurface of the substrate having the alignment material coated thereon,or the UV irradiation process may be performed at a region where a stepis formed on the substrate having the alignment material coated thereon.That is, when the rubbing cloth fails to contact the substrate, a stepis formed on the substrate, and thus the polarized UV rays may beirradiated to the region where the step is formed (in other words, thepolarized UV rays may be irradiated to the step region while shieldingregions other than the step region with a mask). When the alignment ofthe rubbing cloth becomes disordered and the step forms on thesubstrate, the polarized UV rays are preferably irradiated over theentire surface of the substrate.

When the polarized UV rays are irradiated only on the step regions,different step regions are formed depending on whether the substrate isthe thin film transistor substrate or the color filter substrate. Evenwhen the substrates are the same, the different step regions are formeddepending on whether the LCD device is a TN mode or an IPS mode.

Hereinafter, a preferred embodiment of the invention will be describedin more detail.

FIG. 7 shows a sectional view illustrating an LCD device according tothe embodiment of the invention.

As shown in FIG. 7, the LCD device according to the embodiment of theinvention includes a lower substrate 100, an upper substrate 200,alignment layers 300 a and 300 b formed on the substrates 100 and 200,and a liquid crystal layer 400 formed between the substrates 100 and200.

Although not shown in detail, various modifications can be made in thestructures of the lower substrate 100 and the upper substrate 200depending on the different possible modes of the LCD device.

As such, the lower substrate 100 of the TN mode LCD device includes agate line and a data line crossing each other to define a pixel regionthereon; a thin film transistor formed on a crossing region of the gateline and the data line, the thin film transistor including a gateelectrode, a source electrode and a drain electrode; and a pixelelectrode connected to the drain electrode of the thin film transistor.The upper substrate 200 of the TN mode LCD device may include alight-shielding layer; R, G and B color filter layers formed on thelight-shielding layer; and a common electrode formed on the color filterlayers.

The lower substrate 100 of the IPS mode LCD device may include a gateline and a data line crossing each other to define a pixel regionthereon; a thin film transistor formed on a crossing region of the gateline and the data line, the thin film transistor including a gateelectrode, a source electrode and a drain electrode; a pixel electrodeconnected to the drain electrode of the thin film transistor; and acommon electrode formed parallel to the pixel electrode. The uppersubstrate 200 of the IPS mode LCD device may include a light-shieldinglayer; R, G and B color filter layers formed on the light-shieldinglayer; and an overcoat layer formed on the color filter layers.

In addition, a spacer (not shown) may be formed between the substrates100 and 200 to maintain a cell gap between the substrates 100 and 200. Aball spacer or a column spacer may be used as the spacer.

The alignment layers 300 a and 300 b are formed of a mixture of arubbing alignment material and a UV alignment material.

Preferably, the mixture ratio of the rubbing alignment material and theUV alignment material is in the range of about 1:100 to 100:1. Otherpreferred ranges may include 1:50 to 50:1 and 1:20 to 20:1. If thecontent of the rubbing alignment material becomes too large, lightleakage may increase due to rubbing defects. If the content of the UValignment material becomes too large, afterimage may increase due to lowanchoring energy. Therefore, the mixture ratio of the rubbing alignmentmaterial and the UV alignment material can be selected appropriatelyconsidering the size of the LCD device.

A material that generates a photo-isomerization reaction or aphoto-dimerization reaction by UV rays is preferably used as the UValignment material.

Such a material is preferably a polymer obtained by combining aphoto-reaction group with a polymer main chain, The photo-reaction groupmay be at least one of cinnamoyl based material, a chalcone basedmaterial, a coumarine based material, a maleimide based material, or anazo based material. Copolymers using these materials may also be used.

The polymer main chain is preferably at least one of a polyimide,polyamic acid, polynorbornene, phenylmaleimide, polyvinylalcohol,polyamideimide, polyethyleneimine, polyamide, polyethylene, polystyrene,polyphenylenephthalamide, polyester, polyurethane,polymethylmethacrylate, an azo side-chain type imide, a stilbenemain-chain type imide, coumarine derivatives, and chalcone derivatives.Copolymers using these materials may also be used.

More preferably, the UV alignment material is a compound expressed bythe following chemical formulas 1 to 4.

In the chemical formulas 1 to 4, n and m are integers of 1 or more.

Preferably, the UV alignment material has λmax in the range of about 270nm to 350 nm so as not to generate any decomposition reactions due tothe UV rays. Also, the UV alignment material preferably has hardness notless than 2H, corresponding to hardness of a pencil, so as to withstandthe rubbing process.

The rubbing alignment material is preferably at least one of polyimide,polyamic acid, polyamide, polynorbornene, polyamideimide, polyvinyl,polyolefine, polystyrene, polyacrylate, poly(vinylchloride), polyether,polyester, polythioether, polysulfone, polyethersulfone,polyetheretherketone, polyurea, polyurethane, polybenzimidazole,polyacetal, and poly(vinylacetate). Copolymers using these materials mayalso be used.

More preferably, the rubbing alignment material is at least one of apolyimide compound or a polyamic acid compound expressed by thefollowing chemical formulas 5 to 7.

where R is selected from

X₁ is selected from 0, CH₂,

and m is an integer 1 or more.

where X₁ is selected from O, CH₂,

and m is an integer of 1 or more.

where X₁ is selected from O, CH₂,

and m is an integer of 1 or more.

The alignment layer is preferably formed in such a manner that the UValignment material is located over the rubbing alignment material. Inthis case, since the UV alignment material contacts the air, the UValignment material preferably has a polarity lower than the rubbingalignment material.

Also, in order to mix the rubbing alignment material with the UValignment material well, it is preferable that surface tension of eachmaterial is low. Preferably, the surface tension of each material is inthe range of about 30 to 60 dyne/cm considering contact with thesubstrate. If the UV alignment material is located over the rubbingalignment material, the surface tension of the rubbing alignmentmaterial may be preferably equal to or greater than that of the UValignment material.

FIGS. 8A to 8E are process views illustrating a method of fabricating anLCD device according to a preferred embodiment of the invention.

First, as shown in FIG. 8A, a lower substrate 100 and an upper substrate200 are prepared. The detailed construction of the lower substrate 100and the upper substrate 200 and the method for forming them can bevaried by various methods.

Afterwards, as shown in FIG. 8B, alignment layers 300 a and 300 b arecoated over the lower substrate 100 and the upper substrate 200.Although the alignment layers 300 a and 300 b are formed over bothsubstrates 100 and 200 in the drawing, they are not limited to thiscase.

Since the alignment layers 300 a and 300 b are formed of the samematerial as discussed above, a detailed description of the material willbe omitted here.

The coating of the alignment layers 300 and 300 b is accomplished byprinting the alignment layers over the substrates 100 and 200, followedby curing the printed alignment layers.

The step of printing the alignment layers is preferably performed byspin coating or roll coating after dissolving the alignment component inan organic solvent. Other types of coating methods, such as gravurecoating, may also be used.

The step of curing the printed alignment layers is preferably performedby twice curing at a temperature range between about 60° C. and 80° C.and between about 80° C. and 230° C.

Afterwards, as shown in FIG. 8C, a rubbing process is performed on thesubstrates 100 and 200 coated with the alignment layers 300 a and 300 b.Rubbing a rubbing roll 500, attached with a rubbing cloth 520, in thedesired alignment direction, performs the rubbing process.

Then, as shown in FIG. 8D, polarized UV rays are irradiated to thesubstrates 100 and 200 where the rubbing process has been completed,using a UV irradiation device 600.

The UV irradiation process may be performed after the rubbing process.However, it should be noted that the invention is not limited to thissequence. Thus, the rubbing process may be performed after the UVirradiation process, or the rubbing process and the UV irradiationprocess may be performed simultaneously.

The rubbing process and the UV irradiation process are performed suchthat the alignment direction of the alignment layers according to therubbing process becomes identical with the alignment direction of thealignment layers according to the UV irradiation process.

The UV rays may be irradiated over the entire surface of the substrates100 and 200, or only on the step regions where steps are formed on thesubstrates 100 and 200.

If the display is a TN mode LCD device, the step may be formed at aregion for the gate line, the data line, and the thin film transistor onthe lower substrate 100. If the display is an IPS mode LCD device, thestep may be formed at a region for the gate line, the data line and thethin film transistor and a region for the pixel electrode and the commonelectrode over the lower substrate 100. Therefore, the UV rays may beirradiated to the step region while shielding regions other than thestep region with a mask.

Preferably, the irradiation wavelength of the polarized UV rays is inthe range of about 270 nm to 400 nm, and the irradiation energy thereofis in the range of about 50 mJ to 5000 mJ.

As for the polarized UV rays, partially polarized UV rays or linearlypolarized UV rays may be used.

Additionally, the polarized UV rays may be irradiated obliquely orvertically to the substrate. In the case of oblique irradiation, theirradiation angle is preferably about 60° or less. Irradiation of thepolarized UV rays may be performed by a scan type light exposure methodor by an entire light exposure method.

Afterwards, as shown in FIG. 8E, the substrates 100 and 200 are bondedto each other.

The step of bonding the substrates 100 and 200 to each other may beperformed by a vacuum injection method or a liquid crystal droppingmethod.

The vacuum injection method injects the liquid crystal using thepressure difference under the vacuum state after bonding the substrates100 and 200 to each other. The liquid crystal dropping method is to bondthe substrates to each other after dropping the liquid crystal onto anyone of the substrates. As the size of the substrate increases, theliquid crystal dropping method is preferred since the vacuum injectionmethod requires an increased liquid injection time, resulting in reducedproductivity.

The LCD device fabricated in accordance with the invention has thefollowing advantages.

First, since the rubbing process and the UV irradiation process areperformed using the mixture material of the rubbing alignment materialand the UV alignment material, high anchoring energy is obtained throughthe rubbing process, thereby failing to generate afterimage. Inaddition, since the UV irradiation process is performed, the LCD devicedoes not suffer from the problem of light leakage generated when thearrangement of the rubbing cloth is disordered or when the rubbing clothfails to contact the substrate in the rubbing alignment method.

Moreover, since the polymeric material that generates thephoto-isomerization reaction or the photo-dimerization reaction is usedas the UV alignment material, the UV irradiation process does notgenerate photo-decomposition products. Therefore, problems relating toafterimages caused by foreign matter and the necessary additionalcleaning do not occur.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the invention withoutdeparting from the spirit or scope of the inventions. Thus, it isintended that the invention covers the modifications and variations ofthis invention provided they come within the scope of the appendedclaims and their equivalents.

What is claimed is:
 1. A method of fabricating an LCD device, comprising: preparing first and second substrates; coating an alignment layer over at least one of the substrates; performing a rubbing process on the substrate coated with the alignment layer; and irradiating polarized UV rays onto the substrate coated with the alignment layer, wherein the alignment layer is foamed of a mixture of a rubbing alignment material and a UV alignment material, wherein the UV alignment material is a compound having any one of following chemical formulas 2 and 3:

wherein n and m are integers of 1 or more, and wherein the rubbing alignment material is a compound selected from a polyimide compound or a polyamic acid compound having the following chemical formulas 5 to 7:

wherein R is selected from the group consisting of

X1 is selected from the group consisting of O, CH2,

and m is integer of 1 or greater,

wherein X1 is selected from the group consisting of O, CH2,

and m is integer of 1 or greater,

wherein X1 is selected from the group consisting of O, CH2,

and m is integer of 1 or greater.
 2. The method as claimed in claim 1, wherein an alignment direction of the alignment layer formed by the rubbing process becomes identical with an alignment direction of the alignment layer formed by irradiating the UV rays.
 3. The method as claimed in claim 1, wherein irradiating the UV rays is performed over an entire surface of the substrate.
 4. The method as claimed in claim 1, wherein irradiating the UV rays is performed only in a region where steps are formed on the substrate.
 5. The method as claimed in claim 1, wherein the rubbing process is performed before the step of irradiating the UV rays.
 6. The method as claimed in claim 1, wherein irradiating the UV rays is performed before the rubbing process.
 7. The method as claimed in claim 1, wherein the rubbing process and irradiating the UV rays are performed simultaneously.
 8. The method as claimed in claim 1, wherein irradiating the UV rays is performed by irradiating partially polarized UV rays or linearly polarized UV rays.
 9. The method as claimed in claim 1, wherein the polarized UV rays have an irradiation wavelength in a range of about 270 nm to 400 nm.
 10. The method as claimed in claim 1, wherein the polarized UV rays have an irradiation energy in a range of about 50 mJ to 5000 mJ.
 11. The method as claimed in claim 1, wherein the UV rays are irradiated vertically or obliquely at the substrate.
 12. The method as claimed in claim 1, further comprising bonding both substrates to each other.
 13. The method as claimed in claim 12, wherein the bonding of both substrates to each other includes dropping a liquid crystal onto any one of both substrates.
 14. The method as claimed in claim 1, wherein a mixture ratio of the rubbing alignment material and the UV alignment material is in a range of 1:100 to 100:1.
 15. The method as claimed in claim 1, wherein the UV alignment material is a material that generates a photo-isomerization reaction or a photo-dimerization reaction by a UV irradiation process.
 16. The method as claimed in claim 1, wherein the UV alignment material has λmax in a range of about 270 nm to 350 nm so as not to generate a decomposition reaction due to the UV rays.
 17. The method as claimed in claim 1, wherein the UV alignment material has hardness not less than 2H corresponding to pencil hardness.
 18. The method as claimed in claim 1, wherein the rubbing alignment material and the UV alignment material respectively have surface tensions in a range of about 30 to 60 dyne/cm.
 19. The method as claimed in claim 18, wherein the surface tension of the rubbing alignment material is equal to or greater than the surface tension of the UV alignment material. 